Abstract: The ultrasoundassisted extraction of total flavonoids from the fruits of Rosa sterilis was carried out.The effects of extraction time,materialliquid ratio,ethanol concentration and extraction number on the extraction rate of total flavonoids were investigated by single factor experiment,and the extraction process were optimized using response surface methodology.The results showed that the optimal extraction conditions were 70 min of extraction time,1:22.39 of materialliquid ratio,52.2% of ethanol concentration,and 4 times of extraction number.Under this optimal condition,the theoretic extraction rate of total flavonoids could reach to 0.828%.According to the actual experiment,the optimum parameters were modified as:extraction time 70 min,materialliquid ratio 1:23,ethanol concentration 52% and extraction number 4 times,and the actual extraction rate of total flavonoids was 0.817% that is close to the theoretic value.The results showed that the response surface method to optimize the ultrasonicassisted extraction of total flavonoids from the fruits of R.sterilis is feasible.Using Vc as a positive control,the antioxidant activities of total flavonoids obtained from above optimal condition were determined by DPPH and ABTS free radical scavenging assays.The SC50 values of total flavonoids against DPPH and ABTS free radicals were 6.75±0.54 μg/mL and 11.43±0.17 μg/mL respectively indicated that the total flavonoids from R.sterilis possesses a significant antioxidant activity than Vc.

Key words: Rosa sterilis, flavonoids, ultrasonicassisted extraction, response surface methodology, antioxidant activity